1. Field of the Invention.
The present invention relates to a radiation detector or an X-ray computer tomography apparatus (to be referred to as an X-ray CT apparatus) having the radiation detector.
2. Description of the Related Art
An X-ray CT apparatus has an X-ray tube and radiation detector. The X-rays generated by the X-ray tube pass through an object to be examined and strike the radiation detector. The detector has a plurality of detection elements for detecting X-rays as an electrical signal. Each detection element includes a phosphor such as a scintillator for converting X-rays into light, and a photoelectric conversion element such as a photodiode for converting the light into charge (electrical signal). Recently, studies have been made to use a semiconductor element, as a detection element, which directly converts X-rays into charge.
A multislice type radiation detector has recently been introduced. The multislice type radiation detector has a plurality of detection element arrays arranged parallel along the slice direction. Each detection element array has a plurality of detection elements arranged in a line along the channel direction almost perpendicular to the slice direction.
This multislice type radiation detector is required to increase the number of detection element arrays. There was a limitation in the number of detection element arrays with the conventional radiation detector. The major factors that interfere with an increase in the number of radiation element arrays of the radiation detector are the inter-connection structure and connection structure. For the sake of descriptive convenience, assume that photodiodes are arranged in an n×m (channel direction×slide direction) matrix. That is, n photodiodes are arranged in the channel direction, and m photodiode arrays are arranged in the slice direction.
A plurality of photodiodes are connected to a plurality of switching elements through a plurality of signal extraction lines. The m signal extraction lines for the m photodiodes arranged in the slice direction are formed in the gap between this photodiode array and the adjacent photodiode array in the channel direction.
The number of photodiode arrays is therefore determined by the number of signal extraction lines that can be formed in the gap between the adjacent photodiode arrays in the channel direction. Although the number of signal extraction lines can be increased by increasing the gap, the area of the sensitivity range of each photodiode decreases in inverse proportion to the increase in gap, resulting in a deterioration in sensitivity.